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Pigeons need to know just two things to avoid collisions

David Williams/-

Human beings sometimes trip or bump into doorframes, but birds (aside from occasional accidents with man-made windows) almost never collide with obstacles in flight. How do they do it?

To answer this question, David Williams captured pigeons in a parking garage at Alewife station and brought them back to his lab at Harvard, where he’d created a 20-meter long obstacle course. The dutiful pigeons flew from one end to the other, and Williams recorded their movements as they dodged between pairs of vertical poles spaced at different widths. Williams, who is now a post-doctoral fellow at the University of Washington, was prepared to see the birds adopt all manner of different flight tactics. “I expected to see a lot of one wing down, one wing out at the side, approach and hesitation, circling around and planning,” Williams says.

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Instead, the birds used just two simple maneuvers: They either chose to go through the openings with their wings “paused” above their bodies, or they went through with their wings folded down against their sides.

Of those two tactics, the pigeons preferred to pause their wings above their heads, because that posture caused them to lose less altitude and left them in a better position to resume normal flight. However, with openings narrower than about 13 centimeters, the birds took a more conservative approach — they’d fold their wings at their sides, which was more disruptive to flight, but also more stable in the event of a collision. With their wings folded, says Williams, “[the birds] are not going to spin out and crash, which is what they’re trying to avoid.”

Ariah Kidder

The research was published in the Proceedings of the National Academy of Sciences in March. It builds on previous work Williams has done that established that pigeons only start to make plans when they get within 3 feet of an obstacle. During hundreds of lab trials in his most recent study, Williams only observed pigeons collide with the poles twice, and in both cases they recovered quickly. It’s a remarkable success rate, built on a simple approach, that’s all the more noteworthy because pigeons are hardly known as top-fliers.

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David Williams

“It’s not some sort of master-planned, high-concept maneuver,” says Williams. “It’s simple maneuvers with robust flight strategies where, if they hit something, it doesn’t perturb them too much.”

Kevin Hartnett is a writer in South Carolina. He can be reached at kshartnett18@gmail.com.

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